Control valve for hydraulic lift truck



March 26, 1963 Original Filed Oct.

G. F'- QUAYLE CONTROL VALVE FOR HYDRAULIC LIFT TRUCK Ticli- Slu 2 Sheets-Sheet 1 INVENTOR. G. F Qua YLE March 26, 1963 s. F. QUAYLE 3,

CONTROL VALVE FOR HYDRAULIC LIFT TRUCK Original Filed Oct. 4, 1955 2 Sheets-Sheet 2 IN VEN TOR.

ATTORNEY United States Patent 3,082,788 CONTROL VALVE FOR HYDRAULIC LIFT TRUCK George F. Quayle, Philadelphia, Pa.,

Yale & Towne Manufacturing Company, Conn., a corporation of Connecticut Original application Oct. 4, 1955, Ser. No. 538,360, now Patent No. 2,940,767, dated June 14, 1960. Divided and this application Dec. 5, 1958, Ser. No. 778,334 2 Claims. (Cl. 137-522) This is a division of my earlier application Serial No. 538,360, filed October 4, 1955, now Patent No. 2,940,767.

My invention relates to a hydraulic truck in which the lifting operation is performed through the actuation of a lever that in turn operates a pump. Trucks of the particular class are well known in the art and numerous patents have issued on various types of constructions. My truck forms a considerable contribution over the prior art since it makes possible the application of lifting forces in a most ingenious and novel manner. The present application relates particularly to the novel hydraulic lifting and lowering mechanism on my truck.

As a feature of my invention, I utilize a single valve mechanism for controlling the hydraulic lifting and lowering mechanism, while simultaneously acting as a relief valve for preventing the application of undue forces through the hydraulic lifting mechanism. As .a further feature, I employ a foot treadle for effecting the positioning of the valve mechanism so that fluid will flow from below a lift ram piston to allow the downward movement of the ram piston and the lowering of a load on the piston. As a more detailed part of this feature, I utilize a gravity device for normally holding a valve against its seat, the foot treadle pressing against the gravity device to hold the valve seated when lifting of the load is required. The movement of the treadle to a lowering position merely Withdraws pressure from the gravity device so that the load may be lowered.

' As a further feature of the invention, when the treadle is not depressed to eflect lowering of the load, its pressure against the gravity device maintains spring pressure against a valve that in turn prevents" the flow of fluid from beneath the'ram piston. However, upon the application of undue forces, the spring will yield, allowing the movement of the valve away from its seat, so that there may be a bypassing of the ram cylinder, as those skilled in the art will fully appreciate.

I have thus outlined rather broadly the more important features of my invention in order that the detailed description thereof that follows may be better understood, and in order that my contribution to the art may be better appreciated. There are, of course, additional features of my invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception on which my disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of my invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of my invention, in order to prevent the appropriation of my invention by those skilled in the art.

Referring now to the drawings:

FIG. 1 shows my novel hydraulic valve utilized on the lifting head of a hydraulic lift truck;

FIG. 2 is a section showing the construction of my valve.

Referring now more particularly to FIG. 1 of the drawings, I indicate generally by the numeral 12 the lifting head of a truck, the head 12' including a casing 14, and

assiguor to The Stamford,

3,082,788 Patented Mar. 26, 1963 a king post 15 which is formed as a hydraulic rarn cylinder. The lifting head casing 14 has an upper portion 16 that forms a reservoir for hydraulic fluid, and the bottom of the casing 14 has a vertical opening 17 in which a medial part of the hydraulic ram cylinder 15 fits, with a lower end of the cylinder positioned below the casing 14. A plate 18 is welded to the upper part of cylinder 15 so as to bear upon the sides of the upper portion 16 of casing 14, and to act as a cover for the fluid reservoir. The lower end of cylinder 15 has a stub shaft 21 on which a wheel mountingbracket 20 rotates, as in my patent, there also being ball bearings 24 through which bracket 20 supports the casing 14.

The ram cylinder 15 has within it a relatively long ram piston 30 which is somewhat smaller than the bore of cylinder 15 whereby to leave a space around the piston, the lower end of the piston being equipped with a bearing sleeve 31 that slides in cylinder 15. Passages 31a in the lower end of piston 30 enable fluid to flow past the sleeve 31 between the sides and end of piston 30. A medial part of cylinder 15 has a series of ports 36 that communicate with an outer peripheral channel 37, and channel 37 in turn communicates with a bore 40 that is formed at opposed sides of cylinder 15 in the lower part of casing 14. A pump P that I show diagrammatically in FIG. 1 is adapted to apply fluid pressure through a passage 43 to the bore 40, and therefore through the ports 36 and 31a to cause lifting of the ram piston 30 in the cylinder 15. I believe it will be unnecessary to go into further detail as to features of the lifting head 12, since those features are well described in my patent,

re CC of which this application is a division. However, it may be observed that the fluid pressure applied between pump P and-ram piston 30 will also be applied through the peripheral channel 37 on the cylinder 15 to the left-hand portion of the bore 40, as viewed in FIG. 1.

v'alve61 through a gravity member 64 that is adapted to slide vertically in a bracket portion 65 on fluid reservoir 16. This gravity member 64 has a hollow lower end portion 64a positioned about valve 61 and arranged in guide relation to the valve body 62, but with clearance whereby fluid can flow from valve 61 into the reservoir 16. In the hollow end portion 64a I utilize a coil spring 66 that presses a sliding plunger 67 toward the valve 61 for pressing the valve to seated position on valve body 62. For reasons that will appear, I equip the upper end of the plunger 67 with a stop portion 67a for limiting the movement of the plunger 67 and so arranged that spring 66 willnot press the plunger substantially beyond the point that is necessary to seat the valve 61.

The pressure of spring 66 is such that it can hold the valve 61 seated until the fluid pressure in passage 40 develops to a predetermined point, and will yield when the pressure rises beyond that point. Thus, through the operation' of the pump P, FIG. 1, the fl'uid pressure will move the ram piston 30 upwardly to effect lifting, but, should the piston be overloaded, the fluid pressure will move the valve 61 from its seat whereby to relieve the "pressure applied to the ram.

I effect a further control of the valve 61 through the gravity member 64, and I prefer to utilize for the purpose a treadle 70, shown in FIGS. 1 and 2. This treadle 70 is pivoted to the reservoir cover 18 through a pivot 71, and has at one end a screw 72 that is aligned with the upper end of the gravity member 64. A coil spring 73 acts against the treadle 70 for pressing the screw 72 against the gravity member 64. The spring pressure that is thus applied to the gravity member 64 is suificient to hold the member in a depressed position even when the pressure relief spring 66 yields. However, by moving the treadle 70, the truck operator can relieve the gravity member 64 from the spring pressure that is applied through screw 72 to the gravity member 64. This will relieve also the pressure that the gravity member 64 applies through spring 66 to the valve 61, since the plunger 67 limits the extension of that spring. The fluid pressure acting on valve 61 can then lift the valve (lifting also the gravity member 64 since the weight of that member is less than the force exerted by the spring 66. Thus, the treadle 70 when depressed will effect a discharge of fluid from the ram cylinder 15 to the fluid reservoir and will thereby allow a lowering movement of the piston 30.

I control automatically the speed at which the piston 30 is lowered, utilizing for that purpose an extremely novel flow limiting member 75, well shown in FIG. 2, that I prefer to position in the bore 63 of valve body 62. This member 75 is formed as a rod with its outer peripheral surface 76 maintaining a substantial clearance relatively to the inside of bore 63. Along the rod 75, I form the outer surface 76 with a series of angular grooves 77. When the piston is lowered with no load or a load that is relatively light, the fluid will be discharged rather freely through the clearance around rod surface 76, but the rate of flow will be moderate since the fluid will have relatively low pressure. If we assume, on the other hand, that the load is heavy, the rate of flow will increase somewhat and the grooves 77 will then cause the flow to be more turbulent, thereby absorbing a very considerable amount of energy and restricting the rate at which fluid will discharge from the ram. This arrangement will act when a heavy load is on the piston to prevent a lowering movement that is too fast, yet will not make the lowering movement unduly slow when the piston has little or no load.

I believe that those skilled in the art will now understand the construction and operation of the extremely novel hydraulic truck lifting mechanism that I contribute by my invention. In that mechanism I utilize a control valve that has very considerable advantages acting as both a relief valve and a lowering valve while automatically controlling the lowering speed of the platform under different loads. Thereby I contribute a hydraulic system that is very efficient, but that enables me nevertheless to make the lifting head of the truck quite compact. All of these things I accomplish through a construction that is simple and that has a relatively small number of parts. I believe, therefore, that those skilled in the art will appreciate the very considerable value of my invention.

I now claim:

1. For use is a truck of the class described,

a pressure relief valve for controlling fluid pressure that is applied between a pump and a lifting ram, said valve comprising a body having a bore in communication with a source of fluid pressure.

a valve seat formed about said bore on the valve body,

a valve movable relatively to said seat for discharging pressure from the bore in said valve body,

a control member mounted for movement in aligned relation to said valve and valve seat,

a spring having one end engaged with said control member and an opposed end extending toward the valve,

means for applying said opposed end of said spring to the valve and engageable with the control member to limit the extension of the spring while holding said spring assembled relatively to the control member,

movable holding means for holding said control member in a position in which the pressure of the spring presses the valve against its seat, said spring yielding to effect predetermined relief of the fluid pressure,

and means for moving said holding means for effecting a movement of said control member away from said position, said spring by its assembly to the control member then moving bodily with the control member and freeing the valve from the yielding spring pressure to allow a prompt discharge of fluid pressure past said valve.

2. For use in a truck of the class described,

a pressure relief valve for controlling fluid pressure that is applied between a pump and a lifting ram, said valve comprising a body having an opening in communication with a source of fluid pressure and extending vertically in a direction away from the source of pressure,

a valve adapted to seat about said opening on said valve body and tending to move upwardly away from said opening due to the fluid pressure,

a control member mounted for movement in longitudinally aligned relation to said valve and valve seat,

a plunger mounted for limited sliding on said control member,

a spring assembled between the control member and plunger and pressing the plunger toward said valve,

stop means on said plunger engageable with said control member to limit the extension of said spring movable holding means acting against said control member for holding said member in a lower position in which the pressure of the plunger presses the valve to seated position,

said plunger yielding so that the valve moves to effect predetermined pressure relief,

manual means for moving said holding means to enable the valve to lift the control member from its lower position,

and said plunger then moving bodily with the control member to free the valve from the yielding spring pressure and effecting a prompt discharge of fluid pressure past said valve.

References Cited in the file of this patent UNITED STATES PATENTS 

1. FOR USE IS A TRUCK OF THE CLASS DESCRIBED, A PRESSURE RELIEF VALVE FOR CONTROLLING FLUID PRESSURE THAT IS APPLIED BETWEEN A PUMP AND A LIFTING RAM, SAID VALVE COMPRISING A BODY HAVING A BORE IN COMMUNICATION WITH A SOURCE OF FLUID PRESSURE. A VALVE SEAT FORMED ABOUT SAID BORE ON THE VALVE BODY, A VALVE MOVABLE RELATIVELY TO SAID SEAT FOR DISCHARGING PRESSURE FROM THE BORE IN SAID VALVE BODY, A CONTROL MEMBER MOUNTED FOR MOVEMENT IN ALIGNED RELATION TO SAID VALVE AND VALVE SEAT, A SPRING HAVING ONE END ENGAGED WITH SAID CONTROL MEMBER AND AN OPPOSED END EXTENDING TOWARD THE VALVE, MEANS FOR APPLYING SAID OPPOSED END OF SAID SPRING TO THE VALVE AND ENGAGEABLE WITH THE CONTROL MEMBER TO LIMIT THE EXTENSION OF THE SPRING WHILE HOLDING SAID SPRING ASSEMBLED RELATIVELY TO THE CONTROL MEMBER, MOVABLE HOLDING MEANS FOR HOLDING SAID CONTROL MEMBER IN A POSITION IN WHICH THE PRESSURE OF THE SPRING PRESSES THE VALVE AGAINST ITS SEAT, SAID SPRING YIELDING TO EFFECT PREDETERMINED RELIEF OF THE FLUID PRESSURE, AND MEANS FOR MOVING SAID HOLDING MEANS FOR EFFECTING A MOVEMENT OF SAID CONTROL MEMBER AWAY FROM SAID POSITION, SAID SPRING BY ITS ASSEMBLY TO THE CONTROL MEMBER THEN MOVING BODILY WITH THE CONTROL MEMBER AND FREEING THE VALVE FROM THE YIELDING SPRING PRESSURE TO ALLOW A PROMPT DISCHARGE OF FLUID PRESSURE PAST SAID VALVE. 